Put images next to or above your AdSense block can help improve your clicks-rate.Edit: take note, however, to make it clear that the images are not part of the ads. If not sure, consult AdSense support before doing this.

Use channels to track the performance of different format, colors, and positions.

Opt in for both image ads and text ads. Google will choose better performing ads for you.

AdSense have both CPM (cost per thousand impressions) and CPC (cost per click) ads, and will choose the one it thinks can perform better.